1. Field of the Invention
This invention relates to a method for drying a gas by means of adsorption on a desiccant able to be regenerated, according to which method a gas is sent through a first amount of this desiccant, while a portion of the dried gas is sent through a second amount of already used desiccant for regenerating it, this gas portion for the regeneration being heated and after having taken up moisture is evacuated, whereby, after regenerating the second amount of desiccant, the gas flow is inverted so that the gas to be dried is sent through the regenerated second amount of desiccant, while a portion of the dried gas is now sent through the first amount for regenerating.
2. Discussion of the Related art
Methods of this kind are used amongst others for drying compressed gas, mostly compressed air. The compressed gas leaving the compressor has a relatively high moisture content. Part of the moisture is separated by cooling this air. The remaining moisture may be disadvantageous for the conducts and is undesirable for some applications.
A known method of this kind is disclosed amongst others in EP-A-0.419.433. The compressed air to be dried is dried in a first column, while the wet desiccant is regenerated in a second column by a portion of the dried compressed air. This portion is introduced, at half-height of the column, in the lower end of a tube mounted axially in the column and containing an electrical heating element. The gas is heated in the tube and flows in the wet desiccant at the top of the column, flows downward and leaves, charged with moisture, the column at the bottom.
It is evident that this heated gas causes a heating of the desiccant. Heated desiccant is however less effective than cold desiccant and therefore the regenerated desiccant is normally cooled before being used again for drying. If the desiccant is too hot when it is used for drying, a regeneration will start instead of drying. Cooling is also necessary to avoid dew point pikes during drying.
In said known method, this cooling is obtained by turning off the electrical heating while a portion of the dried compressed air is still sent through the desiccant.
In this way, the cooling can only take place after the complete regeneration of the desiccant and consequently the complete regeneration and cooling process is time-consuming. Moreover, an additional amount of already dried air is required for the cooling and is lost for consumption. This increases the energy consumption.